Since 1971 the Environmental Protection Agency and the Center for Disease Control have cooperated in the investigation and reporting of waterborne outbreaks in the United States. Three hundred and twenty waterborne outbeaks affecting 77,989 individuals were reported during 1971-80 by 43 states and Puerto Rico. Three deaths were associated with these outbreaks. Thirty-five outbreaks and 4,450 cases of waterborne disease were reported in 1981. Most outbreaks occurred in noncommunity water systems but most of the disease resulted from outbreaks in community water systems. There is a seasonal distribution of outbreaks in noncommunity and individual water systems with most outbreaks occurring in the summer months and affecting primarily travelers, visitors to recreational areas, campers, and restaurant patrons.